Revision of the Silurian and Early Devonian chonetoidean brachiopods of southeastern Australia

Abstract

Thirty-eight species of ostensibly chonetoid brachiopods (some under open nomenclature) have been described from the Silurian and Lower Devonian rocks of southeastern Australia, although most are neither widely distributed nor abundant. Descriptions of many have been based on inadequate material, and in one significant case (Johnsonetes australis) the original material is lost, necessitating selection of a neotype to resolve formally the identity of that species in comparison with the similar species J. culleni. In this systematic revision the known species are redescribed and where possible their generic positions and possible synonymy determined; three are rejected from the Chonetoidea. Silurian taxa include Strophochonetes melbournensis, S. kemezysi n.sp. and 'Protochonetes cf. minimus. Early Devonian faunas are much more diverse. Lochkovian species are S.? savagei n.sp., S.? psiloplia, 'S.' cresswelli, Parachonetes robustus, and the poorly known 'Chonetes' ruddockensis. 'Strophochonetes' cresswelli and P. robustus are also found in the Pragian, along with Asymmetrochonetes? planata, Parachonetes baragwanathi, P.? bowieae, P.? suavis, Septachonetes micrus, 'Chonetes' taggertyensis and 'Chonetes' foedus. The youngest species in the region are Emsian: Johnsonetes australis, J. culleni, J. latus, Septachonetes melanus, Parachonetes buchanensis, P. spooneri, P. konincki and P. flemingi. No species is currently known to be sufficiently widely distributed geographically and sufficiently restricted stratigraphically to be of clear biostratigraphic use. Several former species are junior synonyms. Strophochonetes melbournensis includes Chonetes infantilis, and Johnsonetes australis includes Chonetes teicherti. Parachonetes robustus, the namebearer for Gill's 'robustus gens', certainly includes both Chonetes killarensis and C. productoida. It is likely that the two other species of this group, P. baragwanathi and P. buchanensis, are also synonymous but, for lack of appropriate specimens, this cannot be conclusively established. The Cambrian Chonetes concinna, subsequently (and wrongly) referred to Eoorthis, is refigured and confirmed as not being a chonetoidean. Chonetes gaskini is shown to be the ventral valve of a spiriferid, and Chonetes bipartita has already been assigned to the sowerbyelloid Plectodonta.